Jan. 7, 2009 -- More than a third of babies born by planned, repeat C-section in the U.S. are delivered before 39 weeks gestation, and these babies are at increased risk for birth-related health problems as a result, a study shows.
These days, nearly one in three births in the U.S. is a cesarean delivery, up from around one in five births in the mid-1990s. The increase is largely because far fewer women who have had C-sections are attempting vaginal births for subsequent pregnancies.
National figures show that 40% of the 1.3 million cesarean deliveries performed each year in the U.S. are repeat procedures and the majority of these are planned.
In the absence of medical need, planned, elective C-section before 39 weeks gestation is not recommended by the American College of Obstetrics and Gynecology (ACOG), unless testing shows that the baby's lungs are mature enough for delivery.
Due Date Minus 7
The new study shows that 36% of planned cesarean births were performed before 39 weeks.
Researchers tracked more than 24,000 repeat C-section deliveries performed at 19 of the nation's top teaching hospitals.
They found that:
- Just under one in three deliveries (29.5%) was performed at 38 weeks and 6% were performed at 37 weeks.
- Babies delivered in their 37th or 38th week had a higher incidence of birth-related adverse outcomes, including respiratory problems and sepsis (serious infection), than babies delivered in their 39th week.
- Compared to babies delivered during their 39th week, babies born between 38 and 39 weeks gestation had up to double the risk of adverse birth-related complications; babies born between their 37th and 38th weeks had up to a fourfold increase in risk.
The study appears in the Jan. 8 issue of the New England Journal of Medicine.
"There appears to be a window of safety that is smaller than has generally been thought," obstetrics professor and study co-author John M. Thorp, MD, of the University of North Carolina, Chapel Hill tells WebMD. "A woman's due date minus seven days seems to be the optimal time for a planned C-section."
Alan Tita, MD, PhD, who led the research team, tells WebMD that the number of women in the U.S. who are having early, planned C-sections may be even higher than the study suggests.
That's because the women in the study gave birth between 1999 and 2002, and the rate of cesarean deliveries has increased since then.
Convenience Driving Early Delivery
Why are so many women having C-sections before 39 weeks of gestation?
Women who were insured, older, and married were the most likely to have early, planned deliveries, the study shows. In an editorial accompanying the study, Massachusetts General Hospital director of obstetrics Michael Greene, MD, wrote that these women are more likely to place a premium on their own doctor delivering their babies.
"To accommodate busy schedules and to minimize the chance that a patient will begin labor and require a non-elective procedure when her doctor might not be available, procedures are frequently scheduled just before 39 weeks of gestation," he wrote.
Green tells WebMD that most obstetricians probably see no harm in pushing delivery dates back a week or so, and will be surprised by the study findings.
"These findings tell us that when it comes to newborn morbidity, many doctors and their patients are running a yellow light if not a red light," he says.
Physicians may also be feeling pressure from hospital administrators to perform planned C-sections at specific times.
Tita points out that the rate of early, planned, C-section deliveries ranged from a low of 18% to a high of 50% at the hospitals participating in the study.
"This indicates that some of this was driven by the institutions," he says.
Thorp says he tries to perform planned, uncomplicated cesarean sections in the 39th week, but he admits that it is sometimes a challenge.
"I would have loved to have performed the two that I did this morning at the end of last week," he says. "That would have fit my schedule better and it would have made my patients happy. But they hadn't quite reached 39 weeks."